1. Field of the Invention
The invention relates to an apparatus for sterilizing liquids by means of ultraviolet rays, wherein the radiation source used is a low pressure, high current, mercury vapour lamp (UV lamp) which is provided with an appendix-shaped piece of tube (appendix) located on the discharge tube.
2. Description of the Prior Art
Apparatus for sterilizing liquids, which utilize ultraviolet radiation sources, are disclosed, for example, in German Offenlengungsschrift No. 2,630,496 and U.S. Pat. No. 3,637,342. In cases where the discharge tube of the UV lamp possessed an appendix for creating the mercury vapour pressure, the space in which the UV lamp was fixed was, in the previously used apparatus, divided essentially into three thermally mutually separate chambers, namely a bottom chamber, in which was located the "appendix" of the UV lamp, a middle chamber, in which was located the discharge space of the lamp, and a round chamber in which the liquid to be sterilized flowed, and an upper part which accommodated the electrode bulbs and which was cooled by cooling fins. The three-chamber division appeared necessary so that on the one hand the operating temperature of the discharge zone (as a rule .gtoreq.300.degree. C.) did not excessively heat the appendix which, being the coldest point (as a rule .ltoreq.65.degree. C.) of the system, is responsible for the mercury vapour pressure and hence also for the radiation intensity, while on the other hand the upper space was also not excessively heated by the discharge zone, since this space, which is accessible from the exterior, was, for safety reasons, not allowed to become excessively hot.
In order that the UV lamp should be able to "strike" at all, the entire appendix section had to be preheated by means of a resistance heater before striking the lamp. On switching on the anode current, this heating was again switched off. In operation, the temperature of the appendix was determined by the heat fed back from the discharge zone, and by the temperature of the surrounding air. This in turn varied with the water temperature. The temperature of the appendix therefore had to be corrected, depending on the time of year, by using suitable spacers by means of which the appendix was lowered to a greater or lesser degree into the bottom chamber.
The previous apparatus suffered from the disadvantage that on heating the appendix in order to strike the lamp, the middle part, and hence the discharge zone, remained cold. Hence, the mercury was able to recondense there, which made it more difficult for the lamp to strike. On the other hand, the high temperature of the discharge zone in the middle chamber during operation was extremely detrimental to the life of the UV lamp.